506. STAN – A New Concept in Aircraft Weight and Balance

Paper

Abstract

Fairchild Controls and Pan American World Airways have developed a simple means of measuring the takeoff gross weight and determining the center of gravity of loaded aircraft. The system, called STAN, for summed total and nose gear, receives inputs from pressure transducers mounted in landing gear oleos, and provides digital cockpit readouts.
In its present form, the system is accurate to + 0.5% or better. It can tell the pilot where his lateral center of gravity is and indicate proper setting for the horizontal trim stabilizer in addition to his actual Take-Off Gross Weight (TOGW) and longitudinal Center of Gravity (in Percent MAC).
Development of STAN began when Pan American World Airways asked us to build a system of pressure transducers and indicators which could measure pressures in the oleo struts of a DC-7C and display these pressures on cockpit mounted gauges. The object was to investigate the possibility of using this data as a safety check against manual computations of take-off gross weight and center of gravity.
The prototype system was operationally tested by Pan American over a period of three months. Results showed that the system’s accuracy at 1.5 percent had to be improved. Provisions had to be made against error caused by cross-wind gusts but this was believed of much lesser importance in heavier aircraft. Otherwise the system worked perfectly and required no maintenance during its test program.
Pan American then asked us to refine the system incorporating digital servo indicators in place of the psi indicators used the prototype, plus a change in the type of transducer used to improve the accuracy, eliminate any need for heaters, and provide long life. Following extensive engineering effort, the system was designed, built and delivered to Pan American who are now currently installing it aboard a 707C aircraft for an exhaustive test program. This Operational Test System is redundant incorporating dual pressure transducers on each gear, a selector switch to switch from Set 1 to Set 2, a voltmeter and transducer selector switch for checking out each transducer individually plus several other refinements. The Operational Systems which will be supplied to Pan American following their test program will be non-redundant and much of the test circuitry will be dispensed with, making the system highly simple to operate and maintain.
In addition to Pan American, Fairchild has also proposed systems to other domestic and foreign airlines and aircraft manufacturers plus designing special STAN systems for the C-5A design concepts proposed by Douglas, Boeing and Lockheed. This new aircraft, which may eventually become a commercial transport, will gross in at over 700,000 pounds or approximately twice the weight of the present jet airliners. It is virtually certain to have a STAN system, or comparable method for measuring its weight and CG, aboard.